Caliper (thickness) measurement can be critical for understanding process impacts in the act of creating products made from sheet materials. For example, in the context of a box product made from a corrugated fiberboard sheet material, the caliper of the sheet material correlates with board stiffness and load carrying capacity and, thus, box performance characteristics. For that reason, it is a critical process parameter in the manufacture of such products. Similarly, caliper is an important process parameter that is considered in the manufacture of other products from sheet materials, such as, for example, paper, paperboard, corrugated fiberboard, plastic, corrugated plastic, combinations thereof, and/or the like.
Conventionally, caliper measurement is a manual process. As sheet material is being processed, for example, a small number of sheets are removed and manually measured by a caliper device or, in some instances, by destructive testing. For instance, to manufacture a corrugated box container, manual measurements are typically obtained at a corrugator once combined board is formed, again before that combined board is converted into a box, and finally once the manufacture of the box has been completed. This process is labor intensive and time consuming. As such, only a limited number of products can be inspected. Indeed, it is not uncommon for an entire run of thousands of boxes to be characterized by one or, at most, a handful of caliper measurements to assess the impact of the process on the corrugated board from which the boxes are made.
Past attempts to improve the process of measuring caliper have been largely unsuccessful for a number of reasons. Generally, such attempts required restraint of the sheet material against a fixed and stable portion of an apparatus (e.g., to align the sheet with a measurement device and/or provide a reference point from which to measure). Yet, the process of restraining the sheet materials introduces substantial inefficiencies (i.e., significantly slowed processing speeds) and risks additional damage to the sheet material from the restraining contact. Other attempts to measure caliper of sheets in motion were generally frustrated by the frequent and erratic movement of the sheets along the transport path due to, for example, vibrations, mechanical processing impacts, aerodynamics, etc.